1. Field of the Invention
The present invention relates to a throttle control method for an internal combustion engine. More particularly, the present invention relates to a throttle control method wherein the degree of opening of the throttle valve is controlled by a motor, and the throttle valve and the motor are connected to each other and disconnected from each other by a clutch mechanism.
2. Description of the Related Art
The throttle valve of an internal combustion engine is arranged to control the output of the internal combustion engine by controlling either the fuel-air mixture in the case of a carburetor or the intake air quantity in the case of an electronically controlled fuel injector, in association with an accelerator actuating mechanism including an accelerator pedal connected to the throttle valve.
The accelerator actuating mechanism has heretofore been mechanically coupled to the throttle valve. There has recently been proposed an apparatus wherein the throttle valve is opened and closed in accordance with the operation of the accelerator by a driving means which is interlocked with a driving source, for example, a motor. For example, Japanese Patent Laid-Open Publication (KOKAI) No. 55-145867 (1980) discloses an apparatus wherein a stepping motor is coupled to the throttle valve and driven in accordance with the operation of the accelerator pedal. Japanese Patent Laid-Open Publication (KOKAI) No. 59-153945 (1984) discloses a similar apparatus.
It is, however, unclear in the above-described related art how to check as to whether or not each device, for example, a motor constituting the throttle control apparatus, is functioning normally. Generally, the motor and other constituent elements are individually checked, and when any of them is judged to be abnormal, the throttle control is suspended and the driver is informed that there is an abnormality in the throttle control apparatus. However, some functions of the constituent elements of the throttle control apparatus, for example, the operating function of a throttle sensor, cannot be checked when the motor and other associated devices are in an inoperative state. Accordingly, it is necessary in order to check the operating function of each device to detect an operating condition of the motor and other devices. To detect an operating condition of each device, the throttle valve must be opened and hence the rotational speed (RPM) of the internal combustion engine is undesirably raised, which makes the driver feel uncomfortable. There is also a fear that the vehicle speed will be uncontrollably increased.